Manufacturing process and heat dissipating device for forming interface for electronic component

ABSTRACT

A method includes preparing a bonding surface of a heat dissipating member, applying flux to the bonding surface of the heat dissipating member, and removing excess flux from the bonding surface so that minimal flux is provided. The method also includes preparing a die surface of an electronic device package, applying flux to the die surface, and removing excess flux from the die surface so that minimal flux is provided. The method further includes positioning a preform solder component on the die surface, positioning the heat dissipating member over the die surface and the preform solder component such that the flux layer of the bonding surface is in contact with the preform solder component, and reflowing the solder component using a reflow oven. A heat spreader is also described for use in the process.

FIELD

The technology described herein relates to a manufacturing process forapplying a solder thermal interface material for use in high heatelectronic devices. The technology described herein also relates to anew and useful heat spreader.

BACKGROUND

Semiconductor circuit processing has seen dramatic improvements thatallow semiconductor manufacturers to shrink the size of circuits formedon wafers. This shrinkage provides a cost advantage to the manufacturerbecause more circuits can be provided in a given area of a wafersurface. Semiconductor circuits generate a lot of heat caused byresistance to electricity running through the circuits. As densityincreases, the amount of heat generated also increases. Heat build upcan impact the performance, reliability, and durability of electricalcomponents. Thus, an efficient heat removal system is necessary.

Heat dissipating devices, such as heat spreaders, have been used todissipate heat from electronic components. These devices draw heat awayfrom the electronic components and spread it over a larger area forfurther heat removal. Surface contact between the heat dissipatingdevices and the electronic components is a factor in determining howefficiently the heat dissipating devices operate. Thermal conductivitybetween surfaces is related to the surface area that is in directcontact. Because surfaces of heat spreaders and electronic componentsare not perfectly flat or smooth, it is difficult to achieve perfectcontact between surfaces. Because air is a poor thermal conductor, anyair pockets between the surfaces can inhibit heat dissipation. Toovercome this problem, thermal interface materials have been used tofill gaps between surfaces.

A variety of materials have been used as thermal interface materials,including phase change materials and metallic solder. The use ofmetallic solder can result in improved conductivity, but processes fortheir application to component surfaces have their drawbacks. Achievinga durable bond in the soldering process may involve reflow of thethermal interface materials. In addition, heating temperatures necessaryto appropriately heat the solder may damage the electronic components.

Prior implementations of solder thermal interface materials (STIMs) usedfluxless soldering in a vacuum oven in order to minimize voids in theSTIM. One type of material that has been used in these fluxlesssoldering operations is Indium. Specialized equipment and knowledge wasrequired in this process. Prior implementations also required themetallization of a silicon die at the die level. This required that thecomponent manufacturer perform the operation. In addition, many priorimplementations required STIM soldering prior to or coincident with massassembly reflow. These prior methods often resulted in an impermanentbond between the STIM and the electronic component, which wasundesirable. Fluxless bonding methods are known to have low throughputand involve high costs, which can make them unsuitable for high volumesemiconductor manufacturing. Other prior implementations involved theuse of flux, but the flux was known to cause voids, which resulted inreliability issues.

SUMMARY

In accordance with the teachings described herein, a method comprisespreparing at least two bonding surfaces on one or more of a lowersurface of the heat dissipating member, a die surface, or a lower or anupper surface of a preform solder component, preparing a mating surfaceon one or more of the lower surface of the heat dissipating member, thedie surface, or the lower or the upper surface of the preform soldercomponent, and applying flux to the bonding surfaces. The method alsoincludes removing excess flux from the bonding surfaces so that minimalflux is provided, positioning the preform solder component on the diesurface, positioning the heat dissipating member over the die surfaceand the preform solder component; and reflowing the solder componentusing a reflow oven. The flux layers on the bonding surfaces arepositioned between both the preform solder component and the die surfaceand the preform solder component and the heat dissipating member.

The bonding surfaces may be the die surface and the lower surface of theheat dissipating member. Alternatively, the bonding surfaces may be thedie surface and the upper surface of the preform solder component. Thebonding surfaces may be the lower surface of the preform soldercomponent and the upper surface of the preform solder component, or thebonding surfaces may be the lower surface of the preform soldercomponent and the lower surface of the heat dissipating member.

The method may further include aligning tabs that are positioned on theheat dissipating member with the electronic device package in order toproperly position the heat dissipating member on the electronic devicepackage. Standoffs may be positioned on the heat dissipating member thatextend from a lower surface of the heat dissipating member and have aheight that promotes squeeze out of the preform solder component whenthe heat dissipating member is positioned over the electronic devicepackage.

The electronic device package may be a BGA package and the method mayalso include providing a die component and metalizing the die componentat the BGA package level, including cleaning and masking the BGA packageand metalizing any exposed die surfaces. Metalizing may include applyingat least one layer of gold. The method also includes assembling the BGApackage onto a circuit card prior to preparing the die surface of theBGA package, and checking the metallization adhesion to the die.

The electronic device package may be a BGA package assembled on acircuit card assembly, and the method may also include providing a diecomponent and metalizing the die component at the circuit card assemblylevel, including cleaning and masking the circuit card assembly andmetalizing any exposed die surfaces. The metalizing step may includeapplying at least one layer of gold. The metalizing step may includeapplying a first layer of titanium followed by a second layer of gold.Prior to metallization, the method may include cleaning the exposedsilicon die and BGA package with an etching process. The etching processmay utilize argon (Ar) plasma.

The flux utilized in the process may be a diluted flux. The method mayinclude removing excess flux by absorbing any excess flux with anabsorbent medium.

The method may also include applying a heatsink weight to the heatspreader. The heatsink weight may be positioned on top of the heatspreader during reflow in order to promote squeeze-out of solder of thepreform solder component and for even temperature distribution over thepreform solder component. The method may also include applying a secondweight to the heatsink weight and removing the second weight prior toreflow heating. Reflow heating may occur in a standard reflow oven. Themaximum temperature of heating in the reflow oven may be such that theelectronic component assembly's temperature is lower than about 20degrees C. below the melting point of the electronic component assemblysolder.

In another aspect of the invention, A heat spreader includes a bodyhaving a substantially flat upper surface and a substantially flat lowersurface, gold plating in at least an area on the lower surface of thebody that is for aligning with a die and a solder component of anelectronic device package, and standoffs extending from the lowersurface of the body and having a height that promotes squeeze-out of asolder thermal interface material when the heat spreader is positionedover an electronic device package.

The standoffs are support surfaces that mate with an edge of anelectronic device package. The heat spreader may be nickel plated on atleast part of its external surface and may have a width and a lengththat is greater than a width and a length of an electronic devicepackage.

The heat spreader may include alignment tabs for aligning the heatspreader with the outside edges of an electronic device package. Thealignment tabs may be defined to substantially abut the edges of theelectronic device package. The heat spreader may be etched on an uppersurface of the body that coincides with the location of a die when theheat spreader is positioned over a die on an electronic device package.The heat spreader may have low surface roughness in the area of the goldplating.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a top view of a die/BGA package utilized in connection withthe example method;

FIG. 2 is a cross-sectional side view of the die/BGA package of FIG. 1;

FIG. 3 is a top view of a die/BGA package having a tape dot installedfor use with pick and place equipment and/or storage;

FIG. 4 is a perspective top view of an example heat spreader;

FIG. 5 is a top view of the heat spreader of FIG. 4;

FIG. 6 is a cross-sectional side view, taken at line 6-6 in FIG. 5, ofthe heat spreader of FIG. 4;

FIG. 7 is a bottom view of the example heat spreader of FIG. 4;

FIG. 8 is a side view of the example heat spreader of FIG. 4;

FIG. 9 depicts a jar of flux including a pick applicator for use inapplying flux to the example heat spreader and die/BGA package;

FIG. 10 is a view of flux being applied to the lower surface of theexample heat spreader with the applicator;

FIG. 11 is a view of a lint free swab being used in a loop to removeexcess flux from the example heat spreader lower surface;

FIG. 12 depicts a plurality of indium solder preforms positioned in astorage box;

FIG. 13 depicts a spatula for use in moving the indium solder preformsto the die surface;

FIG. 14 depicts the spatula being used to position an indium solderpreform on the die surface;

FIG. 15 depicts properly aligned solder preforms positioned on the diesurface;

FIG. 16 depicts improperly aligned solder preforms positioned on the diesurface;

FIG. 17 depicts a bottom surface of a weight that is for application toan example heat spreader, with the weight incorporating an adhesivestrip with a backing in place;

FIG. 18 depicts the bottom surface of the weight with the backing of theadhesive strip removed;

FIG. 19 depicts the top surface of the heat spreader showing the diepattern engraved on the top surface thereof for assistance in placingthe heat spreader on a die;

FIG. 20 depicts a first finned weight applied to the top surface of theheat spreader;

FIG. 21 depicts a side view of the heat spreader and weight beingpositioned on a die/BGA package;

FIG. 22 depicts a perspective top view of a heat spreader and finnedheatsink weight positioned on a die/BGA package;

FIG. 23 depicts the positioning of a weight block on the heat spreaderand the heatsink weight depicted in FIG. 22;

FIG. 24 depicts an x-ray image of an acceptable bond between a heatspreader and a die showing slight solder spill-over;

FIG. 25 depicts an x-ray image of an acceptable bond between a heatspreader and a die showing minor voids in the solder where the voidstotal less than 5% of the overall area of the die;

FIG. 26 depicts an x-ray image of an unacceptable bond between a heatspreader and a die showing incomplete die contact and a void in thesolder; and

FIG. 27 depicts an x-ray image of a bond between a heat spreader and adie showing spill-over bulging from the die, which could cause shortingand needs to be evaluated further before it can be deemed acceptable.

DETAILED DESCRIPTION

The technology described herein relates generally to a manufacturingmethod and heat spreader design for coupling a heat spreader to anelectronic component, such as a die, using a solder thermal interfacematerial (STIM). The solder thermal interface material is implementedfor high heat electronic devices to significantly reduce operatingtemperatures of the die and associated electronic device package. Thedisclosure herein provides a process for permanently attaching ametallic solder layer to a bonding surface of a heat dissipating deviceand to a surface of a die.

Increasing heat dissipation and density of components requires thecontinued exploration of new materials for cooling. Indium is utilizedherein as a material to use as a solder for the thermal interfacematerial. Indium has a thermal conductivity that is much greater thanpreviously used thermal interface materials. For example, indium has athermal conductivity of about k=86 W/m ° K while phase change materialmay have a thermal conductivity in the range of about k=1-10 W/m ° K.Indium has a significantly lower thermal resistance and a higher thermalconductivity than prior thermal interface materials. The example processuses minimal flux to reduce voids, which allows the use of a standardreflow oven and standard reflow knowledge. The process providessignificant thermal performance benefits. The example method describedherein involves the reflow soldering of a STIM between a metalized dieon a ball grid array (BGA) package along with a custom designed heatspreader in order to significantly decrease semiconductor junctiontemperatures and allow higher performance at a given ambienttemperature.

An electronic device package 10, such as a die/BGA package, for use withthe example process and example heat spreader 12, is shown in FIGS. 1and 2. A die 14 is positioned on a BGA substrate 18 to form theelectronic device package 10, also referred to herein as die/BGA packageor BGA package. When the terms die/BGA package or BGA package areutilized herein, it should be understood that any type of electronicdevice package is intended, not limited to a BGA substrate. The BGAsubstrate 18 includes solder balls 20 for mounting with a printedcircuit board. The die 14 is surrounded by underfill 22. While a singledie is shown, it should be noted that multiple dies on a single packagemay also derive significant benefit from the invention.

FIGS. 4-7 depict an example heat spreader 12 that has a top surface 26,a bottom surface 28, alignment tabs 30 and standoffs 32. Standoffs 32incorporate support surfaces 38 and outer legs 40. The top and bottomsurfaces 26, 28 of the heat spreader 12 are substantially flat and arenot warped. The bottom surface 28 includes a gold metalized pad 34 thatcoincides with the location of the underlying die surface 14 when thepackage 10 is assembled. The top surface 26 includes an etched orengraved pattern 36 which depicts where the underlying metalized goldpad 34 is located. The alignment tabs 30 are located along the top andbottom edges of the bottom surface 28 of the heat spreader 12 and extenddownwardly therefrom. The standoffs 32 are positioned along the sides ofthe heat spreader 12 and have a support surface 38 that is designed forabutting an upper surface of the electronic device package 10. The outerlegs 40 of the standoffs 32 are designed to extend along and abut theouter edge of the underlying electronic device package 10. The alignmenttabs 30 are also designed to extend along and abut the outer edges ofthe electronic device package 10. The heat spreader 12 has dimensionsthat are greater than the dimensions of the electronic device package 10so that the heat spreader 12 may fit over the electronic device package10.

In one example, the heat spreader is nickel plated on all or part of itsexternal surfaces and a layer of gold is applied to all externalsurfaces. Alternatively, the heat spreader may be nickel plated on allor part of its external surfaces, with a layer of gold only positionedon the bottom surface of the heat spreader. Alternatively, the heatspreader may be nickel plated on all or part of its surfaces and have agold layer positioned only in the area where the heat spreader contactsthe die. Other coating combinations may be utilized. Other types ofcoating materials may also be found to be useful.

The example process begins with the provision of a die on a substrate 18by an electronic component manufacturer. Once the die is provided, thedie can be metalized at the BGA package level. An example of a die isshown in FIGS. 1-2, which depicts a BGA package 10 having a singlesilicon die 14. As discussed above, multiple dies of the same ordifferent sizes may be positioned on a single package 10.

The surface of the die 14 is prepared and inspected before further workis performed. The top surface of the die is checked for any surfaceirregularities or defects that may be detrimental to metallizationoperations. Defects are determined by examining the die surface undermagnification.

If any defects are detected in a die 14, the surface of the die 14 iscleaned with acetone and a lint free swab and then reinspected. Ifsurface defects are detected that are deemed detrimental formetallization, the die 14 is not utilized. Once the surface is deemedacceptable, the surface of the die 14 is prepared using an argon oxygenplasma etch process to further remove any foreign contamination that maybe present and that could lead to coating defects. For example, theArgon etching may occur at 200 W, 50 mT, 30SCCM 02 and 8SCCM of AR for120 seconds. Other etching processes may alternatively be used.

The example process involves metalizing the silicon die 14 at the ballgrid array (BGA) package level, which requires cleaning and masking ofthe entire BGA package 10. This allows for the metallization and STIMsoldering of any exposed die 14 part, not just the electronic componentsthat the component manufacturer may provide as metalized. This approachalso allows for metallization and STIM soldering of modules such asgraphics cards, among other modules.

After cleaning, all areas around the die 14 are masked or protected fromany metal deposition such that only the desired parts of the BGA package10 are exposed. Precautions are also taken to avoid damaging the silicondie 14, the die underfill 22 or any other areas of the package 10.Minimal vertical pressure is applied to the substrate during the maskingprocess so as not to deform the solder balls of the BGA package 10.

The silicon die 14 may then be metalized, an example of which is shownbest in FIG. 2. The die 14 is first coated with a layer of titanium (Ti)16, which is followed by a layer of gold (Au). The layer of gold (Au) isthe uppermost surface of the die 14.

One composition for the metallization layers for the titanium base layer16 may have a thickness of about 1000 A+/−25 A. One composition for thegold layer may have a thickness of about 5000 A+/−50 A. Othercompositions may be used if desired. Gold (Au) on Nickel (Ni) ontitanium (Ti) may alternatively be utilized. Other metallizationcompounds may alternatively be used.

The surface of the die 14 is then inspected for scratches and chips. Die14 should not be used if it exhibits large edge chips, such as thosewith a size of 0.015×0.30 inches or larger. The die 14 is wiped cleanwith a control wipe that is lint free and may be dipped in isopropylalcohol. The alcohol should be allowed to evaporate. The componentsubstrate should also be checked to confirm that it is not warped.

Once all metal deposition layers have been completed, it is desirable toperform an adhesion test using a semi-conductive tape with a siliconeadhesive in accordance with ASTM-D3359-09 Test Method “A” (withoutscribing the surface). An acceptable tape that may be used is McMasterCarr #7649A91. Other tapes may alternatively be used. Acceptablecriteria for the metal deposit layers are no peeling or removal.

A Kapton (polyimide) pad (tape dot) 44, such as shown in FIG. 3, may bepositioned on the metalized die surfaces. The tape dot 44 serves as apick up location for the vacuum nozzle of pick and place equipment. Thepad 44 may be 5 mil thick and have a silicone adhesive backing and beeither 1″ round or 1″ square, the size being dependent upon the size ofthe die 14. The tape dot 44 also provides a conformance check formetallization adhesion to the silicon.

After metal deposition, all loose metal flakes from the depositionprocess that are present anywhere on the device are removed using alint-free swab and acetone, or the like. Special attention is given tothe fillet of underfill 22 around the perimeter of each die 14. Theacetone swab is gently rubbed back and forth on the underfill 22 toremove any loose metal. If the metal is still well adhered, this isconsidered acceptable.

The electronic device package 10 is then assembled, via pick and place,onto its circuit card using standard processes, such as mass assemblyreflow. After mass assembly reflow, the tape dot 44 is removed to checkfor metallization adhesion to the silicon.

After the electronic device package 10 has been assembled to the PCB 68,the heat spreader 12 is used in the second stage of the process and theassembly is manually assembled. The heat spreader 12 is a machined metalplate that is used for transferring heat. It may be copper that isnickel plated, with gold interface pads 34. Other materials and coatingsmay alternatively be utilized.

The heat spreader 12, which may be custom-designed, has features thatassist in STIM soldering. The heat spreader 12 may be nickel plated forcorrosion protection and to provide a soldering surface for the STIM.Other materials/coatings may alternatively be utilized, if desired. Theheat spreader 12 may be gold plated in the area to be soldered toimprove wetting of the STIM during reflow. Alternatively, the entirebottom surface of the heat spreader or the entire exterior surface ofthe heat spreader may be gold-plated. The heat spreader 12 has lowsurface roughness in the area to be soldered.

As discussed above, the heat spreader 12 includes standoffs andpositioning features. The heat spreader standoffs 32 have a heightsetting feature 38 that promotes slight squeeze out of the STIM whenmelted. The standoffs 32 are sized and located to minimize the effect ofBGA package warpage, which could otherwise result in no squeeze out orthe creation of too large a gap between the die 14 and the heat spreader12, leading to insufficient solder coverage. The containment oralignment features 30 and 40 help to keep the heat spreader 12 alignedover the electronic device package 10 during STIM melting.

The heat spreader 12 may be checked for burrs along the edges of itssurfaces to ensure that no damage has occurred to the gold interfacesurfaces 34. The heat spreader 12 may also be inspected to confirm thatthe gold covered surfaces are adequately covered. For example, if asurface is missing less than 1% of the gold surface, it is acceptable.The heat spreader 12 can be positioned so that it contacts theelectronic device package 10 on two sides and to check for anynoticeable warpage of the electronic device package 10 or of the heatspreader 12.

Once the heat spreader 12 sides have been checked, the surfaces of theheat spreader 12 can be cleaned using a lint free wipe wetted withalcohol. The gold surfaces on the heat spreader are wiped to remove anycontaminants such as finger oils, leaving no lint. The top edges of theelectronic device package 10 should be clean, especially in the areasinterfacing with the heat spreader 12. In addition, the die surfacesshould be cleaned in a similar manner by wiping with a lint free wipethat is wetted with alcohol to remove any contaminants, such as fingeroils, leaving no lint.

The next step in the process is to apply flux 44 to the bonding surfaceof the die 14 and heat spreader 12. Using a prepared flux mixture 46,shown in FIG. 9, diluted flux is applied to the metalized die bondingsurface 14 using a rod 48, shown in FIG. 10 in connection with the heatspreader 12, and excess flux is removed using absorbent media, such as alint-free tissue in a loop 50 or other media, shown in FIG. 11 for theheat spreader 12, such that minimal flux is present. Any liquid fluxshould be removed after 10 seconds and within an additional 30 seconds.Minimal flux is enough flux to cover the area in a thin layer and istypically applied in a diluted form. One type of diluted flux has aratio of 10 parts isopropyl alcohol to 1 part rosin-based flux. Otherratios for diluted flux may also be used, such as 5:1, 20:1 or othervariations above, below, or in between. Other types of fluxes may alsobe used, such as no-clean flux and organic flux, among others.

The tolerance of flux and alcohol measured can be +/−10%. Flux insufficient quantities is required in order to promote good fusion of theindium solder to the metalized surfaces without creating voids or gasbubbles.

After removal of the liquid flux, only a very thin flux layer and noapparent liquid should be seen. Lint on the die 14 may be removed with aprecut wipe in a loop 50. If any pressure is needed, the die 14 and therest of the component will need to be cleaned off with a full wipe withalcohol and the flux process repeated. If flux is allowed to dry forover a minute, too much will remain for the process and the part willneed to be cleaned off with a full wipe with alcohol and the fluxprocess repeated. To avoid issues with increased flux concentration byevaporated alcohol, the flux mixture should be discarded after 35 days.

Flux is then also applied to the bonding surfaces of the gold areas 34on the lower surface 28 of the heat spreader 12, as shown in FIG. 10.Flux 46 is spread over the gold plated areas 34 of the heat spreader 12.After 10 seconds and within an additional 30 seconds, the liquid flux isremoved using a pre cut control wipe held in a loop 50, as shown in FIG.11, such that minimal flux remains. After removal of the liquid flux,only a very thin flux layer and no apparent liquid should be seen. Ifflux 46 is allowed to dry for over a minute, too much will remain forthe process and the part will need to be cleaned off with a full wipewith alcohol and the flux process repeated.

The next step in the process is to position a solder thermal interfacematerial (STIM) preform on the metalized die 14 surface. The preform isa consistent flat rectangular piece of indium metal that issubstantially the same size as the die 14 to which it is being applied.Indium preforms 52 may be provided in a storage case 54, as shown inFIG. 12. The preforms 52 may be picked up with a special spatula 56 thatis attached to an x-actor knife blade holder, shown in FIG. 13. Thepreform 52 is flipped or slid onto the spatula 56. Folding or scratchingof the surface of the indium preform 52 should be avoided. Then theindium preform 52 is slid onto the pre-fluxed component die 14, as shownin FIG. 14.

Proper alignment of the preform 52 on the die 14 involves being able tosee the edge of the die 14 around the edge of the preform 52. FIG. 15depicts properly aligned preforms 52 while FIG. 16 depicts improperlyaligned preforms 52. If the preform 52 overhangs the die 14 by more than0.005 inches, placement is not proper. One type of preform 52 that isutilized can be 0.01″ thick. Indium preforms 52 are delicate and must bekept clean. Indium preforms 52 typically will melt at 157 degrees C.,which is below tin-lead and lead free solder melting temperatures.

The next step in the process involves positioning a heat spreader 12 onthe component die 14 and positioning a heatsink weight 58 on the uppersurface 26 of the heat spreader 12. The heatsink weight is a firstweight that is applied to the upper surface 26 of the heat spreader 12and acts to improve heat transfer during the reflow process and alsoacts to promote squeeze-out of the indium preform during reflow. Theheatsink weight 58 has a strip of thermal tape 60 that has a backing 62,as shown in FIG. 17. When the backing 62 is removed, as shown in FIG.18, the heatsink weight 58 may be applied to the top surface 26 of theheat spreader 12. The heatsink weight 58 may be finned, as shown in FIG.20.

A die 14 outline may be etched or engraved 36 on the top surface 26 ofthe heat spreader 12 in order to assist in orientation of the heatspreader 12, as shown in FIG. 19. Using this outline, the heat spreader12 may be oriented over the die 14 so the gold area 34 on the heatspreader 12 is located over the die 14 surface. The heatsink weight 58is then positioned on the heat spreader 12, which will cover theengraving 36 on the top surface of the heat spreader 12. The doublesided thermal tape 60 on the heatsink weight 58 is installed to keep theheatsink weight 58 from moving. Then the heat spreader 12 is loweredonto the component die 14 by aligning the alignment tabs 30 and theouter legs 40 of the heat spreader 12 to fit around the outside edges ofthe electronic device package 10, as shown in FIGS. 21 and 22. Thealignment features 30 and 40 prevent excessive movement of the indiumpreform 52 on the die 14, particularly since the engraving on the heatspreader is no longer visible.

Once the heat spreader 12 is positioned on the electronic device package10, a second weight, such as a block weight 64, shown in FIG. 23, may bepositioned on top of the heat spreader 12 center to compress the preform52 to assist in contact between the flux coated surfaces. The block 64can be removed after 5 seconds. The block may be, for example, a 1.3 kgblock. The second weight ensures contact between the indium solderpreform, the die, and the heat spreader.

Once the heat spreader 12 and die/BGA package 10 are assembled, theentire assembly is then positioned in a standard reflow oven (notshown). The assembly may be positioned on a conveyor chain, such as onconveyor chain pins. Where a conveyor is not used, the assembly maysimply be positioned in an oven. The STIM is melted at temperatures thatare less than or equal to the melting point of the electronic componentassembly solder minus about 20 degrees. For example, for an assemblysolder with a melting point of 200 degrees C., the STIM is melted atabout 180 degrees C. or lower. Then the assembly is allowed to cool andthe heatsink weight 48 is removed.

After the assembly has been heated, the assembly is completed and it isnecessary to check for defects. An x-ray may be taken to look fordefects. Voids seen in x-ray images 66 that appear to be greater than 5%of the indium soldered die surface area are considered to be defective.Due to the heat spreader 12, printed circuit board 68, back sidecomponents (not shown but similar to 10) and processor construction,x-ray inspection is difficult to determine voiding or contact of theindium with the die 14 and heat spreader 12 surfaces. Spillover isacceptable without voiding. Voids are acceptable if the total number ofvoids covers less than 5% of the die 14 surface area. FIGS. 24-27 depictvarious x-ray images 66 after reflow. FIGS. 24 and 25 depict acceptablevoids 70 and spillover 72. Incomplete die contact that creates a void 74with no spill over is unacceptable, as shown in FIG. 26. Spill over 76of indium that could cause shorting requires further evaluation orinspection in order to insure that no shorting occurs, as shown in FIG.27. When shorting is in question, a microscope may be used to inspectthe indium. In addition, a mirror may be necessary to inspect from viewswhere components block viewing. In addition, the heat spreader 12 shouldbe visually inspected to ensure flatness and proper orientation.

A type of reflow oven that may be used is the Heller 1707EXL. Rework ofthe assembly is generally not possible because the indium solderprovides a permanent bond between the die 14 and the heat spreader 12.Removal of the heat spreader 12 will result in a loss of the goldinterface of the component die. Thus, the heat spreader 12/BGA package10 will need to be replaced if unacceptable defects are identified.

The above description involved applying flux to the bonding surfacespresent on the die and on the heat dissipating member. Alternatively,flux could be applied to the preform solder component. For example, inone example, flux could be applied to the die and to the upper surfaceof the preform solder, so that the flux between the die and preformsolder component is initially positioned on the die while the fluxbetween the preform solder component and the heat dissipating membergold surface is initially positioned on the upper surface of the preformsolder component.

In another example, the flux could be positioned on both sides of thepreform solder component and not initially on the die or on the heatdissipating member gold layer. In this example, the flux between the dieand the preform solder component would be provided by the lower surfaceof the preform solder component and the flux between the die and thepreform solder component and the heat dissipating member would beprovided by the upper surface of the preform solder component.

In yet another example, the flux could initially be positioned on thelower gold surface of the heat dissipating member and on the lowersurface of the preform solder component. In this example, the fluxbetween the die and the preform solder component is provided by thelower surface of the preform solder component and the flux between thepreform solder component and the heat dissipating member is provided bythe flux positioned on the gold surface of the heat dissipating member.These variations provide the user with different options for how andwhen the flux is applied. Moreover, it may be possible to pre-flux thepreform solder component so that it shortens the assembly time, amongother benefits. Thus, the above process description is applicable withany of these examples.

While a heat spreader 12 was discussed above, other heat dissipatingdevices may also or alternatively be utilized, such as heat sinks, heatpipes embedded in heat collectors, and/or any other heat conductingdevices. While a given die configuration was disclosed, other shapes andsizes for the die 14, for the BGA package 10, and for the heat spreader12 may be utilized depending upon the application.

While a lint free swab and wipe are describe in connection with cleaningthe various surfaces of the various components and preforms, any type ofabsorbent media may be used. In addition, cleaning solutions other thanalcohol or acetone may also be used.

While the above-description was generally in the context of ball gridarray packages, other types of integrated circuit package technologiesmay also derive a benefit from the invention described herein. Theseinclude pin grid arrays, land grid arrays, multiple integrated circuitstack-ups and other types of mounting and packaging technologies. Thesetechnologies are collectively included within the term electronic devicepackage 10. In addition, the invention is applicable to a variety ofpackage materials including organic, ceramic, and flex packages.

The term “substantially,” if used herein, is a term of estimation.

While various features are presented above, it should be understood thatthe features may be used singly or in any combination thereof. Further,it should be understood that variations and modifications may occur tothose skilled in the art to which the claimed examples pertain. Theexamples described herein are exemplary. The disclosure may enable thoseskilled in the art to make and use alternative designs havingalternative elements that likewise correspond to the elements recited inthe claims. The intended scope may thus include other examples that donot differ or that insubstantially differ from the literal language ofthe claims. The scope of the disclosure is accordingly defined as setforth in the appended claims.

What is claimed is:
 1. A method comprising: preparing at least twobonding surfaces on one or more of a lower surface of a heat dissipatingmember, a die surface, or a lower or an upper surface of a preformsolder component; preparing a mating surface on one or more of the lowersurface of the heat dissipating member, the die surface, or the lower orthe upper surface of the preform solder component; applying flux to thebonding surfaces; removing excess flux from the bonding surfaces so thatminimal flux is provided; positioning the preform solder component onthe die surface; positioning the heat dissipating member over the diesurface and the preform solder component such that the flux layers onthe bonding surfaces are positioned between both the preform soldercomponent and the die surface and the preform solder component and theheat dissipating member; and then first reflowing the preform soldercomponent to both the heat dissipating member and the die surface usinga reflow oven.
 2. The method of claim 1, wherein the bonding surfacesare the die surface and the lower surface of the heat dissipatingmember, or the bonding surfaces are the die surface and the uppersurface of the preform solder component, or the bonding surfaces are thelower surface of the preform solder component and the upper surface ofthe preform solder component, or the bonding surfaces are the lowersurface of the preform solder component and the lower surface of theheat dissipating member.
 3. The method of claim 1, further comprisingaligning tabs that are positioned on the heat dissipating member withthe electronic device package in order to properly position the heatdissipating member on the electronic device package.
 4. The method ofclaim 3, further comprising standoffs positioned on the heat dissipatingmember that extend from a lower surface of the heat dissipating memberand have a height that promotes squeeze out of the preform soldercomponent when the heat dissipating member is positioned over theelectronic device package.
 5. The method of claim 1, wherein theelectronic device package is a BGA package and further comprisingproviding a die component and metalizing the die component at the BGApackage level, including cleaning and masking the BGA package andmetalizing any exposed die surfaces, and metalizing includes applying atleast one layer of gold; and assembling the BGA package onto a circuitcard prior to preparing the die surface of the BGA package, and checkingthe metallization adhesion to the die.
 6. The method of claim 5, whereinmetalizing includes applying a first layer of titanium followed by asecond layer of gold.
 7. The method of claim 5, wherein prior tometallization, the method includes cleaning the exposed silicon die andBGA package with an etching process.
 8. The method of claim 7, whereinthe etching process utilizes argon (Ar) plasma.
 9. The method of claim1, wherein the electronic device package is a BGA package assembled on acircuit card assembly, and further comprising providing a die componentand metalizing the die component at the circuit card assembly level,including cleaning and masking the circuit card assembly and metalizingany exposed die surfaces, wherein metalizing includes applying at leastone layer of gold.
 10. The method of claim 1, wherein the flux is adiluted flux.
 11. The method of claim 1, wherein the removing excessflux steps include absorbing any excess flux with an absorbent medium.12. The method of claim 1, further comprising applying a heatsink weightto the heat spreader, with said heatsink weight being positioned on topof the heat spreader during reflow in order to promote squeeze-out ofsolder of the preform solder component and for even temperaturedistribution over the preform solder component.
 13. The method of claim12, further comprising applying a second weight to the heatsink weightand removing the second weight prior to reflow heating.
 14. The methodof claim 1, wherein reflow heating occurs in a standard reflow oven andthe maximum temperature of heating in the reflow oven is such that theelectronic component assembly's temperature is lower than about 20degrees C. below the melting point of the electronic component assemblysolder.